In the present state of the art of steelmaking or treating liquid ferrous metals in a converter of the type used in the basic oxygen steelmaking process, there is a clear tendency towards the injection of various gases and powders into the liquid metal through the bottom of such converter by means of a properly designed mechanism and tuyeres for injection. For instance, in some processes for oxygen steelmaking in a bottom blown converter, a plurality of gases and powder must be injected through tuyeres located in the converter bottom. This implies the simultaneous and continuous introduction and transport through the converter passageways of such fluids and solid fines streams in order to accomplish their continuous injection into the liquid metal contained in the converter, even during rotation.
In this type of process, a typical set of flowpaths consists of a line for leading various gases or gas/solid mixtures according to the stage of the process, i.e., oxygen or oxygen/lime mixture, or argon, or nitrogen, or air from such line. The fluids are distributed and finally led to set of bottom converter tuyeres for injection into the liquid bath. In the same typical flow path, a number of lines are used for transporting cooling gases to be injected in the liquid bath through outer annular tuyeres formed by a second pipe evolving from the central nozzle, which as mentioned serves for injection of process gases, i.e. oxygen or oxygen/lime mixture, inert gases, etc.
In this arrangement of double outlets, the annular nozzle injects a cooling gas, preferable hydrocarbon, when the central nozzle is injecting oxygen, so as to protect the whole tuyere from a high temperature rise. In this case it is convenient to have independent flow paths for individual control. This is because in the annular outlet the formation of accretions or metallic deposits is likely to occur, and this results in obstructions of the fluid flow in a given particular line, and hence the necessity of controlling this particular line with no change in the rest of the separated flow paths; for instance, each separated line provided with a flow control valve and check valve; this last one to avoid counter flow of oxygen from the central nozzle when the control pressure exceeds the annular gas pressure and a channeling from center to annular occurs due to metallic deposit in the annular nozzle.
Within the group of technologies for treating molten ferrous metal for producing high quality steel, the ones referred to with combined blowing with bottom injection of gases for agitation of the liquid metallic bath have shown many metallurgical improvements with advantages in cost and operation.
Again in this case, it is convenient to have separated flowpaths for independent control if an optimum performance regarding the injection volumes and specific power of agitation is expected.
A design generation known in the present art of the technology for introducing several fluids into a rotating metallurgical converter is disclosed in U.S. Pat. No. 3,893,658; US. Pat. No. 4,284,266 and U.S. Pat. No. 4,325,540. These rotary joints are based on the principle of concentric tubes for independent flow of fluids through each annular gap formed between tubes when passing from a stationary to a rotating system. The practical inconvenience of these rotary joint designs is that every extra fluid to be introduced requires a corresponding extra tube to form another annular space for fluid transport, and this results in a signifcant increment of size, both in diameter and length of the apparatus. In this regard, an aspect related to the fluid dynamics of the system is the fact that, when the fluids flow into the space formed by concentric tubes in the above mentioned arrangement, the cross section of the conduit is not of a circular geometry; this may result in disturbance of the dynamics of the system like drop of pressure and poor response during control, as when introducing and transporting controlled fluids in a rotating converter, It is desirable to have conduits of circular cross section along the total flow paths up to the point of the injection tuyere outlet.
A stringent condition of transport is the case of pneumatically conveyed powder through a metallurgical converter flow path for injection for instance lime, or carbon bearing powders. These are injected for metallurgical and heat balance control reasons, respectively, and their pneumatic handling imply difficulties in transport and deterioration of hardware due to the abrasive properties of the powdered material; this in turn implies the necessity of adequately designed flow paths. If the introduction and transport of a powder stream into a metallurgical rotating converter follows a flow path configuration similar to a conventionally designed one for pneumatic transport, the performance of the system is better than in the case of a complicated or non-conventional design, for instance in the rotary joint device for introducing the powder/gas mixture from the static to the rotating system. A device known in the art for introducing fluids and a stream of solids into a tiltable metallurgical converter is disclosed in U.S. Pat. No. 4,055,335, in which design the stream of solids pneumaticaly conveyed enters a rotary joint through a lateral opening and flows through an annular space within such rotary joint. In this case, the stream of solids do not follow a typical path used in pneumatic transport of solid fines, and the design for manufacture is not as simple as desired. This Patent also discloses a system for transporting fluids and a stream of solid fines along converter fluid paths, particularly a plurality of concentric passageways in the trunnion shaft central bore radial flow paths from such concentric pipes are also used, with the associated complexity of manufacture and secondary effects on the performance of the solid fines transport.
The present invention is related to a rotary joint mechanism for introducing separated fluids and solid fines, and then a plurality of flow path arrangement in a tiltable metallurgical converter with special design characteristics with improved performance regarding fluid flow and solid transport in the converter passageways, and with a very simple design and construction.